1. Field of the Invention
The present invention relates to a switching power source used for, for example, electronic equipment, and particularly, to a switching power source having a power-factor improving function to improve conversion efficiency.
2. Description of the Related Art
A switching power source apparatus having a power-factor improving converter is used for electronic equipment such as AC adaptors, OA equipment, and consumer equipment, and therefore, must be in compliance with harmonic current regulations (IEC/EN6 1000-3-2) and harmonic suppression guidelines for household and general-purpose appliances. There is a requirement in recent years for a high-efficiency switching power source apparatus capable of contributing to the downsizing and energy-saving of electronic equipment.
FIG. 1 shows an example of a step-up chopper conforming to the harmonic current regulations and serving as a switching power source apparatus. In FIG. 1, a power-factor improving converter consists of a rectifier 2 employing a diode bridge, a switching element 4 turned on and off by a controller 8, and a step-up reactor 3. This step-up chopper controls an ON/OFF switching operation of the switching element 4 so that a peak current of the step-up reactor 3 may follow an input voltage and provide a constant output voltage conforming to the harmonic current regulations.